Modulated reflectance is a technology that has multiple uses for low power RF telemetry and communication applications of many types. A full description of basic modulated reflectance operation is contained in U.S. Pat. No. 6,434,372, issued Aug. 13, 2002, to Neagley et al. One application of this technology is described in U.S. patent application Ser. No. 10/187,025, filed Jun. 28, 2002, by Briles et al., entitled “Remote Down-Hole Telemetry.”
The basic principles of modulated reflectance, as described in the issued patent above, are:                1. The “base unit” sends a carrier RF signal to a “remote unit”, also known as the reflector unit.        2. The “remote unit” modulates the RF signal and reflects a portion of the modulated signal back to the “base unit.”        3. The “base unit” receives the modulated signal from the “remote unit,” completing two-way communication.        
The advantages of the modulated reflectance technology are many, but one of the most important is the fact that the “remote unit” requires either no or minimal power to reflect the signal back to the “base unit.” Therefore, in many cases, the “remote unit” does not require batteries or other sources of electrical power. This is an important advantage for portable or remotely located modulated reflection devices.
These features of modulated reflectance make it of use in many applications. Among these are oil well logging, local-area computer networks, and cell phone related applications. However, the present invention applies the technology in diverse situations in which remote monitoring of persons or equipment without a power source on the remote unit is important.
All of the embodiments disclosed herein are directed toward identification and location methods for persons and property. Although for different applications, each embodiment shares the primary concept of this invention.